1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a plasma display panel that is adaptive for improving discharge efficiency.
2. Description of the Related Art
Generally, a plasma display panel (PDP) is a display device utilizing a visible light emitted from a Phosphor layer when an ultraviolet ray generated by a gas discharge excites the Phosphor layer. The PDP has an advantage in that it has a thinner thickness and a lighter weight in comparison to the existent cathode ray tube (CRT) and is capable of realizing a high resolution and a large-scale screen. The PDP includes of a plurality of discharge cells arranged in a matrix pattern, each of which makes one pixel of a field.
FIG. 1 is a perspective view showing a discharge cell structure of a conventional three-electrode, alternating current (AC) surface-discharge PDP.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes the first electrode 12Y and the second electrode 12Z provided on an upper substrate 10, and an address electrode 20X provided on a lower substrate 18.
Each of the first electrode 12Y and the second electrode 12Z is a transparent electrode made from indium-tin-oxide (ITO). Since the ITO has a high resistance value, the rear sides of the first and second electrodes 12Y and 12Z are provided with bus electrodes 13Y and 13Z made from a metal, respectively. The bus electrodes 13Y and 13Z supply a driving signal from the exterior to the first and second electrodes 12Y and 12Z, thereby applying a uniform voltage to each discharge cell.
On the upper substrate 10 provided with the first electrode 12Y and the second electrode 12Z in parallel, an upper dielectric layer 14 and a protective layer 16 are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer 14. The protective layer 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a Phosphor layer 26. The address electrode 20X is formed in a direction crossing the first electrode 12Y and the second electrode 12Z.
The barrier rib 24 is formed in parallel to the address electrode 20X to prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The Phosphor layer 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive gas for a gas discharge is injected into a discharge space defined between the upper and lower substrate 10 and 18 and the barrier rib 24.
Such a PDP drives one frame, which is divided into various sub-fields having a different discharge frequency, so as to express gray levels of a picture. Each sub-field is again divided into an initialization period for uniformly causing a discharge, an address period for selecting the discharge cell and a sustain period for realizing the gray levels depending on the discharge frequency. For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to {fraction (1/60)} second (i.e. 16.67 msec) is divided into 8 sub-fields SF1 to SF8 as shown in FIG. 2. Each of the 8 sub-fields SF1 to SF8 is divided into an address period and a sustain period. Herein, the initialization period and the address period of each sub-field are equal at every sub-field, whereas the sustain period are increased at a ratio of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field.
FIG. 3 is a waveform diagram of a driving signal applied to each electrode of the conventional PDP.
Referring to FIG. 3, one sub-field is divided into an initialization period for initializing the entire field, an address period for writing a data while scanning the entire field on a line-sequence basis, and a sustain period for sustaining an emission state of the cells into which a data is written.
The first, in the initialization period, an initialization waveform RP is applied to the first electrodes Y. If so, an initialization discharge is generated between the first electrodes Y and the second electrodes Z to initialize the discharge cells. At this time, a misfiring prevention pulse is applied to the address electrodes X.
In the address period, a scan pulse −Vs is sequentially applied to the first electrodes Y. A data pulse Vd synchronized with the scan pulse −Vs is applied to the address electrodes X. At this time, an address discharge is generated at the discharge cells to which the data pulse Vd and the scan pulse −Vs are applied.
In the sustain period, the first and second sustain pulses SUSPy and SUSPz are applied to the first and second electrodes Y and Z. At this time, a sustain discharge is generated at the discharge cells which have generated the address discharge, to thereby display a desired picture on the PDP.
FIG. 4 is a detailed view showing a structure of the first and second electrodes provided on the upper substrate of the PDP.
Referring to FIG. 4, each of the first and second electrodes 12Y and 12Z provided on the upper substrate 10 of the PDP have a width of about 390 μm. The first and second electrodes 12Y and 12Z are formed on the upper substrate 10 at a space of about 60 μm. Further, a distance extending from the first and second electrodes 12Y and 12Z until a boundary portion of the discharge cell is set to be about 210 μm. In other words, the conventional first and second electrodes 12Y and 12Z are provided at the center of the discharge cell. Thus, a sustain discharge generated between the first electrode 12Y and the second electrode 12Z concentrates on the center of the discharge cell. If the sustain discharge concentrates on the center of the discharge cell, then a utility of a discharge space is deteriorated and hence a discharge efficiency is deteriorated.
In order to solve this problem, a space between the first electrode 12Y and the second electrode 12Z may be set widely. In other words, if a space between the first electrode 12Y and the second electrode 12Z is widened, then a discharge path can be lengthened to improve discharge efficiency.
However, a widened space between the first electrode 12Y and the second electrode 12Z causes a rise of a firing voltage and a discharge sustaining voltage to thereby increase total driving voltage.